<!DOCTYPE html>
<html>
<head lang="en">
    <meta charset="UTF-8">
    <title></title>
    <style>
        .one{
            height: 200px;
            width: 200px;
            position: relative;
            background-color: #999999;
        }
        .two{
            position: absolute;
            width: 200px;
            height: 200px;
            background-color: coral;
            border-top-left-radius: 50px;
            border-bottom-left-radius: 50px;
            border-bottom-right-radius: 50px;
            border-top-right-radius: 50px;
        }
    </style>
</head>
<body>
<div class="one">
    <div class="two"></div>
</div>

</body>
</html>